Subterranean wells often include one or more enclosed and/or confined spaces, which may be defined within an annular space between one or more casing sections and/or casing strings and which may contain a variety of fluids. During the course of normal subterranean well operation, pressure within the annular space may vary significantly due to a number of factors, illustrative, non-exclusive examples of which may include the addition and/or removal of fluid from the annular space, changes in the chemical composition of the fluid contained within the annular space, a phase change of a portion of the fluid contained within the annular space, and/or a change in a temperature of the fluid contained within the annular space.
From time to time, pressure variations may result in a significant pressure buildup, or increase, within the annular space. Because subterranean wells may be designed to withstand a specific threshold pressure, pressure range, and/or pressure differential, the pressure buildup in the annular space may present a safety hazard to personnel and/or equipment in the vicinity of the subterranean well, decrease the service life of the subterranean well, and/or lead to failure of one or more components of the subterranean well. As an illustrative, non-exclusive example, one or more of the casing sections and/or casing strings contained within the subterranean well may burst and/or collapse due to this pressure buildup. As another illustrative, non-exclusive example, the structural integrity of other subterranean well components, such as seals, valves, and/or production trees may be compromised by this pressure buildup. As yet another illustrative, non-exclusive example, this pressure buildup may result in physical expansion, contraction, creep, and/or other motion(s) of subterranean well component(s), including vertical growth of the wellhead associated with the subterranean well.
Historically, pressure buildup within the annular space has been managed and/or controlled by such approaches as utilizing one or more of an open casing shoe, monitoring and bleeding of, or releasing, the pressure within the annular space, the use of a pressure relief device, and/or well killing and repair. An open casing shoe may be achieved when a subterranean well is constructed such that there is no seal preventing fluid flow between a terminal, or subsurface, end of a casing string and a portion of a subterranean formation that is proximal that end of the casing string. Thus, the pressure within the annular space at a given depth may be substantially equal to the pressure within the subterranean formation at the given depth. While this technique may be effective at decreasing the potential for pressure buildup within the annular space, this structure must be designed into the subterranean well during its construction and cannot readily be retrofit into existing subterranean wells. In addition, solids and fluids present within the annular space may form a particulate bridge within the annular space, and such a particulate bridge, or barrier, may decrease and/or eliminate the pressure distributing abilities of the open casing shoe. The use of an open casing shoe also precludes the ability to manage and/or control the pressure within the annular space relative to the pressure of the subterranean formation, which may be desirable under certain circumstances, such as to decrease the potential for a flow of fluid into the annular space.
Monitoring and bleeding of the pressure within the annular space may include manual and/or automated monitoring of the pressure within the annular space, together with manual and/or automated venting of the pressure within the annular space should the pressure increase above a target, or threshold, pressure. Monitoring and bleeding is most commonly achieved manually since many subterranean wells cannot be remotely monitored and controlled, making it a labor-intensive process. Since it is typically a manual process, monitoring and bleeding relies on the establishment of a periodic subterranean well inspection strategy, making it both expensive and prone to human error. In addition, and as discussed in more detail herein, particulate bridges may isolate a portion of the annular space, decreasing or eliminating the potential for fluid communication between the wellhead and the portion of the annular space and decreasing the effectiveness of monitoring and bleeding procedures to alleviate pressure buildup within the isolated portion of the annular space.
A pressure relief device may be utilized to automatically relieve annular space pressure if it increases above a predetermined and/or threshold pressure. This typically involves the use of pressure relief devices to relieve and/or equalize pressure in a radial direction, across a casing wall, as opposed to the longitudinal pressure relief techniques described herein. The pressure relief devices are typically built into the casing wall at specific points and often take the form of burst membranes, diaphragms, or other thin-walled portions of the casing that may burst, rupture, or otherwise open if a pressure differential across the pressure relief device increases above the threshold value. Since pressure relief devices are only located at discrete points within the casing wall, they also may be rendered ineffective by the presence of a particulate bridge, as discussed in more detail herein. In addition, since the pressure relief devices typically take the form of a burst membrane, they may be a single-use device that is not able to maintain a potentially desirable pressure differential within the annular space once the pressure relief device has been activated. Furthermore, the presence of the pressure relief device may decrease the overall structural integrity of the casing wall.
Well killing and repair may include any suitable activities adapted to eliminate a hazard associated with pressure buildup and bring the subterranean well back to a safe and functional operational status. These activities are typically invasive in nature, are often labor-intensive, and/or may require that the subterranean well be taken offline for a period of time while the killing and/or repair activities are completed.
While the above systems and methods to manage and/or control the pressure within the annular spaces of subterranean wells may be effective under certain circumstances, they also include a number of significant shortcomings, including those disclosed herein. In addition, several of the above systems and methods may not be practical in circumstances in which access to the wellhead and/or the annular space is restricted, such as may be the case with subsea wells. Thus, there exists a need for improved systems and methods for managing pressures in casing annuli of subterranean wells.